This invention relates to fuel additives for use in large oil-burning furnaces. More specifically, the invention relates to fuel treatment additives useful in reducing boiler fire-side and air heater corrosion, reducing slag formation, facilitating slag deposit removal, and improving fuel combustion efficiency.
As is well known in the combustion art, slag particles form deposits on various surfaces along the combustion path within a furnace. It has been theorized that slag deposits form mainly because of impurities present in the fuel. However formed, these deposited slag particles catalyze known oxidation reactions, such as SO.sub.2 to SO.sub.3. Most furnace fuels contain a variety of sulfur-bearing compounds, because it is not economically feasible to remove such compounds before the fuel is fed to the furnace.
A known product of combustion is water vapor. It is well known that gaseous H.sub.2 O and gaseous SO.sub.3 chemically combine to form H.sub.2 SO.sub.4. As the gaseous H.sub.2 SO.sub.4 concentration builds up in a combustion furnace, the H.sub.2 SO.sub.4 dew point is increased. Slag acts as an absorbent for the condensing H.sub.2 SO.sub.4, thereby aggravating low-temperature corrosion problems. Furnace slag particles are impregnated with condensed H.sub.2 SO.sub.4, and such impregnated deposits can cause significant damage to metallic boilers and other surfaces. Sulfuric acid is not the sole acid formed within combustion furnaces. Other, equally corrosive, acids form and can cause furnace damage through a variety of corrosion mechanisms.
Another well known effect of slag formation inside combustion furnaces is the reduction of furnace heat exchange efficiencies. Reduced efficiencies arise because slag acts as an insulator: its presence on a heat transfer surface reduces the effective rate of heat transfer through that surface.
Generally, slag has a low fusion temperature, and quite often while in a molten state, impacts upon heat exchange surfaces and adheres there. Upon adhering, the molten slag is cooled by the relatively cooler metal of the heat exchange surface and becomes solidified. Such adhering slag can thereafter entrain additional molten slag particles and eventually builds up to become a tenacious deposit.
It is known that certain fuel oil additives interfere with slag formation on furnace surfaces. It has been theorized that such interference is essentially a metal deposition mechanism. For example, certain fuel oil additives furnish a particular metal form of a chemical species at the flame zone of a combustion furnace. Such a chemical species, generally possessing a low energy of activation, then thermally decomposes, thereby furnishing the combustion surface with the deposited active form of a particular metal. The deposited metal then beneficially interferes with the slag formation at the combustion surface. Because of this metal deposition mechanism, the resultant slag is much more friable, does not build up significantly at combustion surfaces, and is likely to be carried off by convective currents within the furnace.
A variety of fuel oil additives, designed to alter or beneficially interfere with slag formation, are known in the art. However, some of these additives are necessarily dual-phase by nature. Prior to the present invention, both an aqueous phase and a continuous oil phase had been required to inject water metal salt solutions into fuel oil.
Dual-phase fuel additives do not disperse well when added to liquid fuels. The poor dispersion of the fuel additive very often results in numerous field problems, such as fouling of oil filters, strainers, and burner surfaces. Such poor dispersion may be caused primarily by the high viscosity of such fuel additives.
In addition to exhibiting poor dispersion qualities, such dual-phase fuel additives are not cost efficient. The active ingredient is generally a water soluble salt. Because these salts are generally dispersed in oil when sold, the dispersed product is necessarily more costly because of the presence of the required oil phase. The present invention is much more cost efficient because no so-called oil phase is required in the commercially available form of the invention. Also, the manufacturing requirements are considerably simplified further lowering cost.
The general concept of a so-called single phase, water-based, salt solution is not new to those skilled in the art. However, prior to the present invention, such products were not commercially useful because they failed to disperse in fuel oil, and, after relatively short periods of time, became unstable.
It is an object of the present invention to provide a completely water soluble fuel oil additive designed to reduce slag formation and increase combustion efficiency. It is also an object to provide such a fuel oil additive which is highly dispersible in fuel oil. It is likewise an object to provide such a fuel oil additive which is stable during storage at storage temperatures which, by way of example, can range from approximately -28.9.degree. centigrade (-20.degree. fahrenheit) to approximately 48.9.degree. centigrade (120.degree. fahrenheit). It is likewise an object to provide such a fuel oil additive that is dispersible in fuel oil and when dispersed is stable with oil for at least 45 days and up to one year.